1. Field of Invention
The present invention relates generally to semiconductor processing equipment. More particularly, the present invention relates to a stage assembly which is suitable for use in a vacuum environment such as a vacuum environment associated with an extreme ultraviolet lithography system.
2. Description of the Related Art
For precision instruments such as photolithography machines which are used in semiconductor processing, factors which affect the performance, e.g., accuracy, of the precision instrument generally must be dealt with and, insofar as possible, eliminated. When the performance of a precision instrument is adversely affected, as for example by contamination, products formed using the precision instrument may be improperly formed and, hence, function improperly. For example, if a photolithography machine which is not designed to operate in a vacuum is used in a vacuum environment, the photolithography machine may cause the vacuum environment to be contaminated. As a result, the vacuum level associated with the environment may be compromised, thereby affecting an overall photolithography process which utilizes the photolithography machine.
Lithography processes, e.g., photolithography processes, are integral to the fabrication of wafers and, hence, semiconductor chips. Systems used for lithography include optical lithography systems, electron beam projection systems, and extreme ultraviolet (EUV) lithography systems. The development of EUV lithography systems is becoming more widespread, as the capabilities of EUV lithography systems generally exceed those of conventional optical lithography systems and electron beam projection systems.
In an EUV lithography system, beams of extreme ultraviolet (EUV) light are reflected off of a reflective reticle, which contains a circuit pattern, onto a semiconductor wafer. Reticle scanning stages are generally used to position a reticle over a wafer such that portions of the wafer may be exposed as appropriate for masking or etching. Patterns are generally resident on the reticle, which effectively serves as a mask or a negative for the wafer. When a reticle is positioned with respect to a wafer as desired, a beam of EUV light may be reflected off of the reticle on which a thin metal pattern is placed and effectively focused onto the wafer.
Many scanning stage devices include a coarse stage and a fine stage which cooperate to position an object such as a reticle or a wafer. Specifically, many high precision machines used in semiconductor fabrication use a coarse stage for relatively large motion and a fine stage for smaller, or more precise, motion. A coarse stage is used to coarsely position a wafer, for example, near a desired position, while a fine stage is used to finely tune the position of the wafer once the wafer is positioned near its desired position by the coarse stage.
In general, an EUV lithography system must operate in a relatively high vacuum environment, which may be expensive to maintain, as any gas leakage into the vacuum environment must be corrected in order to prevent the vacuum level from being significantly compromised. Gas leakage may be associated with air bearings used in many standard EUV lithography systems. Maintaining the vacuum level in a vacuum environment such as a chamber to compensate for gas leakage and other contamination is often difficult or impractical.
As is the case with many scanning stages, the scanning stages used in an EUV lithography system are typically moved using motors such as linear motors. When it is necessary to service the motors, since the motors are positioned within a vacuum chamber, the vacuum chamber is generally opened to enable the motors to be accessed. Opening and closing, i.e., unsealing and resealing, the vacuum chamber is often a tedious process. The accessing of motors within a vacuum chamber exposes the vacuum chamber to contaminants and moisture, which may contaminate the surfaces of components within the vacuum chamber. The moisture within the vacuum chamber generally must be removed before the vacuum chamber may be used again, which increases the time associated with an overall pump down process used to create a vacuum within the vacuum chamber once the vacuum chamber is resealed.
Within a vacuum chamber, it is difficult to maintain an acceptable operational temperature, as motors used to move scanning stages, as for example fine scanning stages, often heat up during operation. When the temperature within the vacuum chamber is too high, the operation of sensors within the vacuum chamber may be compromised. Since there is no air available in the vacuum chamber during an EUV lithography process, the only cooling that is available within the vacuum chamber results from conduction and radiation. As such, maintaining an acceptable temperature within the vacuum chamber is often a difficult process.
Maintaining an acceptable vacuum level and an acceptable temperature within a vacuum chamber is important in order to ensure a high level of performance for an EUV lithography process. Specifically, the ability to efficiently and relatively easily maintain a desired vacuum level and a desired temperature is important.
Therefore, what is needed is a method and an apparatus for providing a relatively easy to maintain EUV lithography system. That is, what is desired is an EUV lithography system which includes a wafer stage device that enables both a desired vacuum level and a desired temperature to be accurately and efficiently maintained.